Justification:
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

This species can be found breeding in northern Scandinavia, the Baltic republics and western Russia to western Siberia, in eastern Siberia, and in the Great Lakes of North America. Its distribution expands in winter to include most of the Mediterranean, Black Sea and Caspian Sea coastlines, as well as the Atlantic coast of Europe and the north-west coast of the U.S.A. (del Hoyo et al. 1996).

The global population is estimated to number c.97,000-270,000 individuals (Wetlands International 2006). The European population is estimated at 23,700-45,200 pairs, which equates to 47,400-90,500 mature individuals (BirdLife International 2015).

Trend Justification: The overall population trend is increasing, although some populations have unknown trends (Wetlands International 2006). In Europe the population size is estimated and projected to be decreasing at a rate approaching 30% over the period from 2000, when the decline is estimated to have started in Russia, which holds nearly 50% of the European population, to 2032 (three generations) (BirdLife International 2015).

Behaviour This species is fully migratory (del Hoyo et al. 1996), usually arriving in its breeding areas from late-April to late-May (Olsen and Larsson 2003) and leaving again in late-July (Richards 1990, Olsen and Larsson 2003) (although its movements are poorly documented) (del Hoyo et al. 1996). The species breeds from late-Junein mixed-species colonies and subcolonies occasionally as large as 2,000 individuals, sometimes also in more solitary scattered pairs (del Hoyo et al. 1996). After breeding the species is gregarious (Snow and Perrins 1998), with groups of 10-20 individuals common at feeding or resting sites (Snow and Perrins 1998), and flocks of hundreds or even thousands congregating briefly at favourable sites or during bad weather (Snow and Perrins 1998). Large groups (thousands of individuals) may also gather on German lakes and wetlands to moult before migrating to wintering areas (Olsen and Larsson 2003). HabitatBreeding The species breeds inland on shallow freshwater and brackish lakes (del Hoyo et al. 1996, Olsen and Larsson 2003), river basins, marshes and bogs (del Hoyo et al. 1996), occasionally also at coastal lagoons (del Hoyo et al. 1996), showing a preference for habitats with lush vegetation (Richards 1990) and emergent or floating plants in muddy shallow water (Snow and Perrins 1998). Non-breeding On migration the species occurs at sea, along shores, and on reservoirs, lagoons and lakes (Olsen and Larsson 2003), wintering along the coast on sandy and muddy beaches (Olsen and Larsson 2003), mouths of rivers (del Hoyo et al. 1996) and at sea (Olsen and Larsson 2003), especially at stream and sewage outlets (Snow and Perrins 1998). DietBreeding The species is mainly insectivorous when breeding, taking e.g. dragonflies, beetles, midges (del Hoyo et al. 1996), mayflies and stoneflies (Richards 1990). Non-breeding On migration its diet is the same as during the breeding season (consisting mainly of insects) (del Hoyo et al. 1996), although during the winter the species switches to a diet of small fish and marine invertebrates (del Hoyo et al. 1996), (Urban et al. 1986). Breeding site The nest varies from a shallow depression (Richards 1990, del Hoyo et al. 1996) to a much more substantial structure depending on the situation (Richards 1990). Nests are sited on the ground in wet vegetation adjacent to or on shallow water (Richards 1990, del Hoyo et al. 1996), floating at the edge of emergent vegetation (e.g. in reedbeds) (del Hoyo et al. 1996), on grassy islands in freshwater shallow lakes (Olsen and Larsson 2003), and occasionally also on sandbanks (del Hoyo et al. 1996). The species breeds in colonies or subcolonies with nests spaced c.1-1.5 m apart, sometimes also in more solitary scattered pairs (del Hoyo et al. 1996).

The species is threatened by habitat degradation, including changes in hydrographic conditions from damming and irrigation works (Rašomavičius 2007, Ellermaa and Linden 2011). It is vulnerable to oil spills (Mendel et al. 2008) and other types of marine pollution, including agricultural run-off (pesticides, biocides) (Ellermaa and Linden 2011). It is vulnerable to being caught as bycatch in fishing gear, including in gillnets (Zydelis et al. 2013). It is considered moderately vulnerable to collision with offshore wind farms (Bradbury et al. 2014) and can be disturbed at sea by shipping traffic.

Conservation Actions UnderwayListed under the African Eurasian Waterbird Agreement and on Appendix II of the Bern Convention. It is listed on Annex I of the EU Birds Directive. It is listed within 106 marine Important Bird Areas within Europe. Within the EU it is listed within 575 Special Protection Areas.

Conservation Actions ProposedIdentification and designation of marine protected areas for important sites at sea. Observer programmes on gillnet fisheries across its range to monitor bycatch rates.